Hydrogen from hydrocarbons



Oct. 9,-1962 .1. E. McEvoY ETAL 3,057,689

HYDROGEN FROM HYDROCARBONS Filed Nov. 14, 1955 rates The presentinvention relates to the production -of hydrogen by the cracking of alow molecular weight normally gaseous hydrocarbon at an elevatedtemperature, and more specifically to a process for cracking a lowmolecular weight normally gaseous hydrocarbon to produce hydrogenutilizing a catalyst comprising iron or an iron oxide impregnated upon aporous solid support, such as kaolin.

The cracking of low molecular weight normally gaseous hydrocarbons suchas natural gas, and in particular methane, to molecular hydrogen iscommonly effected by heating such hydrocarbon to high temperatures. Morerecently, the cracking of such hydrocarbons in the pres ence of metalpebbles, such as pebbles of elemental iron and nickel, ror alloys suchas Inconel or Monel, which metal pebbles serve as heat transfer agents,has been suggested. However, these metallic materials have not provedsatisfactory for this purpose, because they are prone to sinter at thevery high cracking temperatures, such as temperatures of l400 to 2400aF. needed to effect cracking of low molecular weight hydrocarbons toelemental hydrogen. The formation of massive sintered or frittedagglomerates leads to the malfunction of processing equipment and theeventual breakdown and inutility of the process.

A serious difliculty arising from the use of elemental metalliccatalysts, such is iron, for the preparation of hydrogen is theoxidation of such catalysts from the reduced state that is used duringon-streamprocessing to a relatively highly oxidized state during theregeneration stage. Thus, regeneration is effected by the oxidativeremoval through combustion of coke ydeposits from the catalyst. Asconventionally effected, such regeneration causes the oxidation of themetallic catalyst to a metal oxide state. This is most undesirable asthe presence of higher oxides, such as the higher oxides of iron, in thecatalyst during the on-stream cracking of the low mlecular Weighthydrocarbon results in the production of impure hydrogen, namelyhydrogen containing carbon monoxide and carbon dioxide.

Prior commrecial methods for hydrogen production from natural gas haveemployed steam in the conversion to avoid the deposition of coke. Thismethod is likewise unsatisfactory as it results in high carbon oxideproduction. To remove the carbon oxides, which are undesirableimpurities in the hydrogen stream, the hydrogen stream is treated toeffect conversion of the carbon oxides content to carbon dioxide, whichis then adsorptively removed frorn the hydrogen stream by caustic oraqueous solutions under pressure. Such removal is expensive and requires,considerable processing equipment.

This invention has as an object the provision of a method for generatinghydrogen from low molecular Weight hydrocarbons, such as methane.

This invention has as another object the provision of a method forproducing hydrogen of relatively high purity.

This invention has as yet another object the provision of a continuouscatalytic method for the production of hydrogen.

These and other objects are accomplished by the process of the presentinvention in which a natural gas comprising a low molecular weightnormally gaseous hydrocarbon, such as methane, is catalyticallydecomposed to elemental carbon andelemental hydrogen through con-3,057,689 Patented Oct. 9, 1962 tact with a catalyst comprising iron, oriron and `a minor weight percentage of FeO, supported on a porousrefractory solid support, such as kaolin, at an elevated temperature,such as a temperature of about 1400 F. t0 2000 F. or more. A preferredembodiment of the process of the present invention comprises contactinga low molecular Weight normally gaseous hydrocarbon with a catalystcomprising iron, or iron and a minor amount of the lower oxide of iron,namely FeO (such as less than 20 weight percent of the total ironcontent is FeO), impregnated upon a porous support, which catalystcontains not less than about one weight percent of carbon. ln thepreferred embodiment the contact is effected at a temperature of between1500" F. to 1900 F. to convert the hydrocarbon into elemental hydrogenand to deposit coke upon the catalyst to a coke level of not more thanabout five weight percent. The deposited coke is then removed byoxidative regeneration to a coke level in which the catalyst containsnot less than one weight percent of coke.

The oxidative regeneration of the catalyst should be effected in thepresence of relatively high molar percentages `of carbon monoxide, inany event with an amount of oxygen less than-that needed to effectcomplete oxidative removal of the coke. It is desirable that theregeneration be effected with a regenerating gas having a carbonmonoxide to carbon dioxide molar ratio of at least six to one. It hasbeen found that by regenerating th-e catalyst in the presence of gasesrich in carbon monoxide, or containing an insufficient amount of oxygento effect complete removal of the coke from the catalyst, and bypermitting at least one Weight percent of coke to remain upon theregenerated catalyst, and preferably from l =to 3 weight percent, theiron content of the catalyst is not noticeably oxidized to a higheroxide of iron, or at most, oxidized only in minor amount to the loweroxide of iron, such as FeO; and not into Fe2O3 or Fe304.

The avoidance of higher oxides of iron in the catalyst has beenascertained to be necessary because it has been found that the presenceof such oxides in the catalyst tends to produce oxides of carbon duringthe catalytic conversion. On the other hand, the absence of higheroxides `of iron from the catalyst permits the production of hydrogenhaving a purity in excess of and can, if desired, be made to producehydrogen having a purity of or more with less than 2% of carbon oxidesin .the hydrogen product and less than 10% of unconverted low molecularweight hydrocarbons.

ATheinitial catalyst which may be used in the process of the presentinvention may comprise an iron oxide such as Fe203 or Fe304; or mixturesof iron oxide and manganese oxide; and in a preferred embodiment,mixtures of an iron oxide and carbon black; deposited upon a porous andrefractory `solid support, such as kaolin, or diatomaceous earth. Theweight percent concentration of iron is not critical and the ironconcentration in the catalyst may be varied over a wide range, such asfrom 1 to 50 weight percent, although in some cases lower or higherconcentrations of iron may be used. It has been found that catalystscontaining 10 weight percent of iron are particularly useful for thecatalytic conversions of the present invention. A preferred embodimentof the catalyst of the present invention comprises l0 weight percentFe2O3; 20 weight percent carbon black and 70 Weight percent kaolin.

The supported iron oxide catalyst must, prior to being used in thereaction, be heated to reaction temperature such as to l400 F. orhigher, and be reduced to the elemental iron state with but a minoramount of iron in a lower oxide state, by contact with a reducing agentsuch as with a stream of hydrogen.

The reduced iron or ironand lower oxide of iron catalyst may then beused for the conversion of natural gas such as methane or a similar lowmolecular weight hydrocarbon to carbon and elemenal hydrogen inaccordance with the process of the present invention. As set forthabove, this may be accomplished eicaciously at a temperature of between1400 F. and 2000 F. or higher, preferably at a temperature of between1500 F. to 1900 F. and a gaseous hourly space velocity of about 30 to 90to yield hydrogen of relatively high purity. The reaction should becontinued until he coke deposition upon the catalyst reaches the levelof about live weight per cent, at `which time the catalyst should beregenerated.

The regeneration as heretofore noted may be effected with an oxidativegas rich in carbon monoxide, particularly in a gas mixture containingcarbon monoxide and carbon dioxide, in which the carbon monoxide ispresent in a relatively high concentration such as in a ratio of atleast 6:1 in respect to the carbon dioxide, or with carbon monoxidecontaining closely regulated amounts of air. If the molecular oxygencontent is regulated at a low level the combustion products from thecoke on the catalyst will consist of carbon monoxide.

The regeneration should not be effected beyond the stage at which alevel of one weight percent of coke is retained upon the catalyst, sinceit has been found that the retention of coke to this weight percentagelevel serves to prevent the formation of appreciabley amounts of ironoxide on the catalyst `during regeneration. Thus, the residual coke onthe catalyst will tend to reduce the iron oxide formed duringregeneration to elemental iron.

The aforementioned reaction and regeneration stages may be effected in acontinuous process in which a charge comprising a low molecular weightnormally gaseous hydrocarbon is continuously converted to elementalhydrogen.

As illustrative of a preferred embodiment for producing elementalhydrogen of high purity in accordance with the process of the presentinvention, reference should be had to the accompanying schematic flowsheet wherein the flow of the various reactants utilized in the processof the present invention is illustrated. In the accompanying ilow sheet,the hydrogen obtained in the process is utilized as a component in thepreparation of synthesis gas for the manufacture of ammonia. However,the present invention is not restricted to the manufacture of hydrogenfor the preparation of ammonia. Furthermore, it is, of course, to 4beunderstood that the process of the present invention is not limited to`the precise arrangements shown in the accompanying llow sheet, but thatthe details thereof may ybe varied in a manner apparent to one skilledin the art.

The charge for the system comprising a natural gas, such as a naturalgas containing predominantly methane or consisting entirely of methane,is introduced at arnbient temperature through line 10 into preheater 12.

The pretreatment, if any of `the natural gas in line 1t) is dependentupon its source. Thus, the natural gas in line 1) should be low insulphur, carbon dioxide, water vapor and free oxygen. A desired upperlimit for oxygen in all forms is 0.5 weight percent. Thus, t-he naturalgas may be desulphurized or undergo other treatment to render it in aform suitable for use in the process of the present invention.

Within preheater 12 the natural gas is preheated to a temperature ofabout 1150 F. and then conveyed through line 14 to the lower lift hopper16 of a gas lift designated generally by the numeral 1S.

The preheated charge gas in lower lift hopper 16 is joined by spentcatalyst from line 20, which spent catalyst is also at a temperature of1150 F. By spent catalyst as used herein is meant catalyst which hasbeen utilized for on-stream processing and contains the maximum cokelevel of up to about tive weight percent coke.

`In the subject example the catalyst prior to initial coutact with thecharge comprises about ten weight percent of iron impregnated on kaolin,and has a bulk density of one gram per cubic centimeter and a particlediameter of 0.11 inch.

The charge gas serves as the lift gas and elevates the spent catalystfrom lower lift hopper 16 to upper lift hopper 22. From upper lifthopper 22 the lift gas is diverted from the catalyst, and transferredthrough line 24 for on-stream processing as will be describedhereinbelow. The catalyst from upper lift hopper 22 is passed throughline 26 to the upper portion of kiln 28.

Fuel gas, which may comprise gas similar to the charge gas in line 10 isintroduced into the upper portion of kiln 28 from line 30, preheater 32and line 34. The fuel gas is yheated to a temperature of about 1l50 F.in preheater 32 and is thus at about the same temperature as thecatalyst which is introduced into the upper portion of kiln 28 from line26. Air from line 36, preheater 38 and line 49 is also introduced intothe upper portion of kiln 28. The air from line 36 is preferably heatedwithin preheater 38 to a temperature of the order of l200 F. As will bemore fully discussed below, it is necessary to closely regulate theamount of air introduced into kiln 28, as both the coke level on theregenerated catalyst, and the ratio of carbon monoxide to carbon dioxidewithin kiln 28 is dependent upon the amount of introduced air.

The maximum degree of combustion and the highest regenerativetemperature is achieved at the upper part of kiln 28 when the preheatedfuel gas and air Contact the catalyst having the highest coke level.Thus, with a catalyst constituting ten weight percent of ironimpregnated upon kaolin, and having about 4.7 weight percent ofdeposited coke, a temperature of about 21.50 F. will be attained in theupper portion of kiln 28 under the subject conditions. This temperature,which is 1000 F. higher' than the temperature of the catalyst at itspoint of introduction into kiln 28 is not sulhciently high to effectappreciable catalyst breakage by thermal shock for the aforesaid typecatalyst. However, if the support, or the concentration of iron, or theprocessing conditions are varied, the temperature increase in the upperportion of kiln 28 should be regulated so as not to exceed the maximumsudden temperature increase which the catalyst can tolerate.

The catalyst, fuel gas and air pass downwardly in concurrent flowthrough kiln 28, with the carbon level on the catalyst `being graduallydecreased during such downward passage.

At the base of kiln 28 the coke level on the catalyst is approximatelyone weight percent, and the temperature of the catalyst and kiln gasmixture is about 1700" F. To achieve this level of coke reduction underthe aforesaid conditions, it has been found that the air introduced intokiln 28 through line 36 should be such as to yield a carbon monoxide tocarbon dioxide molar ratio of about 20 to 1. Since the carbon monoxidecontent in the kiln gas mixture is determined by the exit kilntemperature, with the higher the temperature the higher the carbonmonoxide content, an increase in the carbon monoxide content of the kilngas mixture can be effected by raising the exit gas temperature.Alternatively, if a higher ratio of carbon monoxide is desired forspecific operating conditions, carbon monoxide may be added to theregeneration gas.

The separation of regenerated catalyst from the kiln gas mixture isachieved by conventional means at the base of kiln 28, and the separatedgas is removed through line 42, Waste heat boiler 44 and line 46 toheat-exchanger 4S. The passage of the gas through waste heat boiler 44and heat-exchanger 48 serves to reduce the temperature of the gas to anominal value. The gas from heatexchanger 48 may be conveyed out of thesystem through line 50 or may be recycled from line 50 to line 30.

The regenerated catalyst from the base of kiln 28 is conveyed throughline 52 to the upper portion of reactor 54. Within reactor 54 theregenerated catalyst is countercurrently contacted with charge gas whichenters reactor 54 from line 24 at the base of reactor 54.

The upward movement of the charge gas through reactor S4 results in itsgradual conversion to hydrogen and elemental carbon, with the carbondepositing on the downwardly moving catalyst.

The cracking of the charge gas constitutes an endothermic reaction withthe heat of reaction being furnished by the downwardly moving catalyst.Thus, during the course of the reaction there is a gradual increase inthe temperature of the rising gas and a corresponding decrease in thetemperature of the falling catalyst Within reactor 54.

The spent catalyst having up to about ve weight percent of cokedeposited thereon is removed from the base of reactor 54 through line20. As heretofore noted, such catalyst when removed is at a temperatureof about 1150 F.

The product gases from the upper portion of reactor 5ftare removedthrough line 56 and when so removed are at a temperature of about 1700F. These product gases may comprise about 96.5 mol percent of hydrogen.about 1 mol percent of carbon monoxide, with the remainder comprisingmainly unreacted methane.

ln the accompanying flow sheet, as heretofore noted, the producthydrogen is converted to synthesis gas for use in the manufacture ofammonia. Thus, the product gas from the upper portion of reactor 54 iswithdrawn through line S6, and nitrogen is supplied to this gas incombustor S8 wherein a controlled partial combustion with air from line60 is eiected, the oxygen in the air being converted to water.

The product gases from combustor 5S are transferred through line 6?. toWaste heat boiler 64 wherein such gases are cooled to a temperature ofabout 600 F.

From waste heat boiler 64 the product gases are transferred through iine66 to methanator 68 wherein the carbon monoxide impurity is hydrogenatedto water and methane. The product gas from methanator 68 is suitablesynthesis gas for ammonia manufacture and after passage through line 70and heat-exchanger 72 wherein it is cooled to 100 F. it may be passed toan ammonia synthesis plant for conversion to ammonia. The maximum amountof carbon monoxide in the synthesis gas product is 0.01 mole percent.

The present invention may be embodied in other speciiic forms withoutdeparting from the spirit or essential attributes thereof and,accordingly, reference should be made to the appended claims, ratherthan to the foregoing specication as indicating the scope of theinvention.

It is claimed:

l. A process for generating hydrogen which comprises contacting a lowmolecular weight normally gaseous hydrocarbon with a catalyst comprisinga porous refractory support impregnated with metallic iron, saidcatalyst containing from 0-20% FeO by weight of the total iron and beingfree of higher iron oxides and said catalyst further containing 1-3% byweight of residual coke; eifecting said contacting at elevatedtemperature between 1400 and 2000 F. to form by decomposition of saidhydrocarbon elemental hydrogen and depositing coke upon said catalyst,continuing said contacting for a period such that the coke content ofthe catalyst is increased to a total content not in excess of 5% byweight of the catalyst, and thereafter regenerating said catalyst byoxidative combustion with air under conditions avoiding excessiveoxidation of the iron therein, the quantity of air used furnishing freeoxygen in an amount insufficient to burn all the coke in the catalystand said regeneration being under conditions such that during combustionof the coke in the catalyst a high molar ratio of at least 6:1 CO/CO2 ismaintained in the vicinity of the catalyst, said regeneration beingcontinued to an extent sufcient to remove a portion of the depositedcoke leaving l-3% by weight of residual coke in said catalyst; andthereafter contacting said regenerated catalyst with additional lowmolecular weight normally gaseous hydrocarbons at said elevatedtemperature to form elemental hydrogen and to deposit coke upon saidcatalyst.

2. A process in accordance with claim l in which the gas supplied forregeneration of the catalyst contains an amount of oxygen related to theamount of coke burned from the catalyst such that the gaseous combustionproduct obtained by said combustion contains carbon monoxide and carbondioxide in the mol ratio of about 20 to 1 CO/CO2.

3. A process for generating hydrogen which comprises contacting methanein a reaction zone with a nonturbulently moving bed of particles ofcatalyst comprising a kaolin support impregnated with metallic iron,said catalyst containing 0-20% FeO by weight of the iron therein andbeing free of higher oxides of iron, said contacting being elfected at atemperature between 1500 F. and 1900 F. to decompose said methane withformation of elemental hydrogen and deposition of coke upon saidcatalyst; continuing said reaction for a period iu which the depositedcoke content of the catalyst is brought to a level not in excess of 5%by weight, then withdrawing said catalyst particles from said reactionzone and conveying said particles by means of gas lift employing methaneas the lift gas to the regeneration zone, regenerating said catalyst insaid regeneration zone by contact with a gas containing free oxygen,thus effecting combustion of the coke deposited therein to a residualcoke level of not less than 1 weight percent of the catalyst,maintaining during such regeneration conditions of temperature andoxygen deficiency such that the ratio of carbon monoxide to carbondioxide in the combustion gas resulting from combustion of said cokeremains in excess of 6 to l; and discharging the said residualcokecontaining catalyst from said regeneration zone to said reactionzone for further contact with methane.

References Cited in the file of this patent UNITED STATES PATENTS2,462,861 Gunness Mar. 1, 1949 2,620,313 Odell Dec. 2, 1952 2,647,041Robinson July 28, 1953 2,783,133 Eastwood Feb. 26, 1957 FOREIGN PATENTS323,855 Great Britain July 27, 1929 380,893 Great Britain Sept. 29, 1932UNITED STATES PATENT OFFICE CERTIFICATE OE CORRECTION Patent No. 3O57689October 9u 1962 James E McEvoy et alo -It is hereby certified that errorappears in the above numbered patlent requiring correction and that thesaid Letters Patent should read as corrected below.

Column lv line20v for v'hydrocarbon" read hydrocarbons line 49 for"commreoal" read commercial ==3 column 2v line TOY after "lower" insertiron --g column 3v line lOv for he read the --0 Signed and sealed this23rd day of July 1963a (SEAL) Attest:

DAVH)L.LADD

Commissioner of Patents ERNEST W. SWIDER Attesting Officer

1. A PROCESS FOR GENERATING HYDROGEN WHICH COMPRISES CONTACTING A LOWMOLECULAR WEIGHT NORMALLY GASEOUS HYDROCARBON WITH A CATALYST COMPRISINGA POROUS REFRACTORY